How to backup through RBX at UNC Path?

Answer:
When you select UNC backup option in RBX then you should use machinename\user in login field. However, if you wish that only username without <machine_name> prefix should work with RBX backup then please keep a note of the following:

If the HCBackup service is running with administrator user logon or rights then simply (username) will work with RBX backup login on UNC path however if you are running HCBackup service with Local System rights then in that case, you would require to exclusively use <machine_name>\username and password.